SPECTROPHOTOMETRIC MEASUREMENT OF THE FIRST DISSOCIATION-CONSTANTS OFCARBONIC-ACID AT ELEVATED-TEMPERATURES

Using 2,5-dintrophenol as an optical indicator, the pH of a carbonate buffer solution was spectrophotometrically measured at temperatures fr om 25 to 175 degrees C. The pH values measured in this study were util ized to determine the first dissociation constant of carbonic acid at various temperatures. The result was pK(1) = - 1234.4 + 68608/T + 193. 37 In T - 0.16423T - 3746800/T-2 where T is in Kelvin. By using this f itted function, the thermodynamic functions for carbonic acid at 25 de grees C were calculated. When the dissociation reaction of carbonic ac id was rewritten as an isocoulombic reaction, the plot of log K-OH aga inst 1/T was approximately linear over the temperature ranges studied, as in other isocoulombic reactions.